This invention relates to an ion beam irradiation system and an ion beam irradiation method for use in a beam processing system using an ion beam or a charged particle beam.
An ion implanter is used in order to implant ions to a circular wafer for semi-conductor device. Generally, a beam generation source, an extraction electrode, a mass analysis magnet, a mass analysis slit, an acceleration/deceleration device, and a wafer treatment chamber are aligned to a beam line in an ion implanter.
Since a cross section of an ion beam is generally smaller than the size of the circular wafer, several methods have been proposed to irradiate such an ion beam to whole of the circular wafer.
As one of the examples for an ion beam irradiation method, it has been proposed that a wafer is scanned with an ion beam to one direction, for example, in a horizontal direction, by a beam deflection scanner for ion beam scan (hereinafter referred to as “fast scan”, “beam scan”, or “X scan”) and a wafer is scanned (moved) to another direction which lies at right angles to the ion beam scan direction, i.e. a vertical direction, by a mechanical Y-scan device (hereinafter referred to as “slow scan” or “mechanical Y-scan”). A whole region of a wafer can be irradiated with the ion beam of a small cross-section size by such combinations of the beam scan and the mechanical Y-scan (see JP-A-2008-262756 (Patent Document 1)).
As shown in FIG. 8, in this type of irradiation method, the scanning width BSW (hereinafter referred to as “beam scan width”) to the X-direction of the ion beam deflected by the deflection scanner is the same in any Y direction region. In other words, the beam scan width at both edges in the Y-direction of a wafer 58 is the same as that in a center region of the wafer 58.
In the irradiation method shown in FIG. 8, since useless ion beam irradiation to outside of the wafer 58 increases as the ion beam irradiation approaches both Y-direction edges of the wafer 58, the beam irradiation efficiency is restricted and hence the productivity of the wafer have some limitations.
As an example for reducing the useless ion beam irradiation to outside of the wafer, it has already been proposed to scan the ion beam with a serrate shape on a wafer (see Japanese Utility Model Registration No. JP-Y2-2548948 (Patent Document 2)).
It should be noted that uniform dose distribution in a whole region of the wafer (hereinafter referred to as “in-plane uniformity of dose amount”) is always required in any ion beam irradiation method.
In the ion beam irradiation method disclosed in Patent Document 2, the wafer is two-dimensionally scanned with the ion beam so that whole irradiation region is reduced to increase beam irradiation efficiency. That is, the ion beam scan in one direction and the ion beam scan in an orthogonal direction are combined and carried out at the same time so that the irradiation region of the ion beam fits the shape of the wafer. In particular, it is configured so that a beam scan pitch of the beam scan becomes constant by configuring the beam scan width of each of the beam scans in one direction so that one direction beam scan, set like steps, is carried out with the same beam scan speed while changing scan period/frequency, while the beam scan speed of the beam scan in the orthogonal direction changes in synchronism with the change of the period of the one direction beam scan. In this irradiation method, although the beam irradiation efficiency can be improved, a target wafer is required to be fixedly set. Therefore, such an ion beam irradiation method can not be applied to an ion implanter which comprises reciprocating wafer moving function by a mechanical Y-scan device, as shown in Patent Document 1.
Further, in the ion beam irradiation method disclosed in Patent document 2, a small fluctuation of ion beam current during ion implantation to a wafer is ignored, which causes unexpected in-plane non-uniformity of the dose amount.